Stars+-+Types

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Rubric: [[file:Space Exploration Adventure Rubric.doc]], [[file:Space Exploration Adventure Rubric.pdf]]
There are many different types of stars in our galaxy, but the main types of stars are variable stars, main sequence stars, star clusters, white dwarfs,red giants, and super giants. In just our galaxy there are thousands of more stars then planets. Star clusters, are clumps of hundreds of stars gathered togther in one area. Variable stars are extremely common, becuase they are stars that vary in their brightness that is shined. Main sequence stars, are charecterized by their source/amount of energy.White dwarf stars are,what stars like the sun are like after they have exhausted their nuclear fuel. Red giant stars, are what stars become like after weak radiation.Finally, Super giants, are the most massive types of stars out in the galaxy, such as the sun.
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Variable stars are stars that vary in brightness over time. In most cases, these changes occur very slowly over a period of months or even years. In some cases, however, the changes take place in a matter of hours. The most common type of variables, with the longest bright-dim cycles, are red giants. Red giants are stars of average size (like our Sun) in the final stages of life. During the last several million years of its multibillion-year lifetime, a red giant expands and contracts many times. It becomes alternately brighter and dimmer, generally spending about one year in each phase until it completely runs out of fuel to burn.

Variable stars are stars that vary in brightness over time. In most cases, these changes occur very slowly over a period of months or even years. In some cases, however, the changes take place in a matter of hours.

Main sequence stars are characterised by the source of their energy. They are all undergoing fusion of hydrogen into helium within their cores. The rate at which they do this and the amount of fuel available depends upon the mass of the star. Mass is the key factor in determining the lifespan of a main sequence star, its size and its luminosity. Stars on the main sequence also appear to be unchanging for long periods of time. Any model of such stars must be able to account for their stability.


 * star cluster ,** a group of stars near each other in space and resembling each other in certain characteristics that suggest a common origin for the group. Stars in the same cluster move at the same rate and in the same direction. Two types of clusters can be distinguished--open clusters, also called galactic clusters because of their wide distribution in our galaxy (the Milky Way), and globular clusters.

Globular clusters radiate with a continuous glow. These nearly spherical (ball-shaped) star systems contain anywhere from tens of thousands to a million stars. They are most heavily concentrated at the center of the cluster. While in reality there is a great distance between stars in these clusters, an observer on Earth may find it impossible to pick out individual stars

A white dwarf is what [|stars] like the Sun become after they have exhausted their nuclear fuel. Near the end of its nuclear burning stage, this type of star expels most of its outer material, creating a [|planetary nebula]. Only the hot core of the star remains. This core becomes a very hot white dwarf, with a temperature exceeding 100,000 [|Kelvin]. Unless it is [|accreting] matter from a nearby star (see [|Cataclysmic Variables]), the white dwarf cools down over the next billion years or so. Many nearby, young white dwarfs have been detected as sources of soft, or lower-energy, [|X-rays]. Recently, soft X-ray and extreme [|ultraviolet] observations have become a powerful tool in the study the composition and structure of the thin [|atmosphere] of these stars.

Because it has run out of fuel, the star begins to cool, and contract. The outer layers of the star fall inwards under gravity, and as they fall they heat up. A **shell** surrounding the central core becomes hot enough to fuse protons into alphas. So the star gains a new source of energy. The core of the star is now hotter than it was during its [|normal life] and this heat causes the outer parts of the star to swell. The star becomes a giant. The radiation from the fusing shell has grown weak by the time it reaches the surface of the star. Weak radiation is red, so the star becomes a **red giant**. Betelgeuse. Image credit: Hubble

If our [|Sun] is an average sized [|star], there are some true monsters out there. They’re the supergiant stars, and they come in two flavors: red and blue. The supergiants are the most massive stars out there, ranging between 10 to 70 solar masses, and can range in brightness from 30,000 to hundreds of thousands of times the output of [|the Sun]. They have very short lifespans, living from 30 million down to just [|a] few hundred thousand years. Supergiants seem to always detonate as Type II supernovae at the end of their lives.